The reliability and applicability of a new, extremely sensitive and specific bioassay for tocopherol (vitamin E) will be increased by: a) determining the conditions which modify the response to tocopherol so that the assay can be more rigorously standardized; b) determining the variance in the results of replicate assays: and c) testing the ability of the assay to detect tocopherol in lipid mixtures. The role of vitamin E in the fertility of female and male rotifers will be determined. If the vitamin is required by the males, as indirect evidence suggests, the proposed ultrastructural analysis of fertile and tocopherol-deficient, infertile testes may provide some insight into the mechanism by which this vitamin affects male fertility in both invertebrates and vertebrates. The striking growth stimulation effect of alpha-tocopherol in female rotifers will be analyzed using cytological, biochemical, and autoradiographic techniques to determine how this vitamin induces cytoplasmic enlargement. The generality of this unstudied effect of tocopherol will be investigated in different organisms and cell cultures. An unknown, probably new vitamin E compound, present in plants both after cutting and senescence, will be purified and identified. The relative biopotency of this compound will be determined in the rat gestation-resorption assay, and information on the derivation and stability of the compound will be obtained.